Recently, an ionomer resin has widely been used as a base resin for a cover of a golf ball (e.g. Japanese Patent Publication No. 49-27093). Particularly, the ionomer resin is exclusively used in a two-piece solid golf ball using a solid core. This is because the ionomer resin is superior in durability, cut resistance and rebound characteristics and, further, it is easily processed.
However, the ionomer resin is inferior in shot feel and control properties (ease of putting spin on the ball) in comparison with a balata used as a base resin for a cover of a thread wound golf ball, because the ionomer resin has a higher hardness and stiffness modulus.
Therefore, a trial has been conducted in order to improve the shot feel and controlling properties by softening the ionomer resin using various means.
For example, in order to improve shot feel and control properties, Japanese Laid-Open Patent Publication Nos. 1-308577 and 5-3913 suggest to soften a high-rigid ionomer resin by blending (mixing) an soft ionomer resin obtained by neutralizing a terpolymer of an .alpha.-olefin, an unsaturated carboxylic acid (e.g. acrylic acid, methacrylic acid, etc.) and an acrylate with sodium or zinc ion.
However, even if the soft ionomer resin as described above is blended, a shot feel similar to that of the golf ball with the balata cover has not been obtained. In addition, there is a problem that rebound characteristics and flight performance are deteriorated by blending the soft ionomer resin.
In addition, in Japanese Laid-Open Patent Publication No. 6-192512, it is suggested that rebound characteristics are improved while maintaining softness by using a mixture of an ionomer resin and a thermoplastic polyamide elastomer. Although the improving effect can also be admitted in view of the maintenance of softness according to this method, it is necessary to improve rebound characteristics and shot feel properties. This is because softness is obtained by increasing the mixing ratio of the thermoplastic polyamide elastomer and therefore the rebound characteristics are lowered a little.
As described above, the golf ball using the ionomer resin as the base resin of the cover is inferior in shot feel and control properties. In addition, the suggestions to improve these properties causes deterioration in rebound characteristics and flight performance and sufficient results have not been obtained.